1. Field of the Invention
The present invention relates to apparatus for manipulating equipment. More particularly, the present invention pertains to apparatus for raising and lowering drill pipe or well casing along a derrick and manipulating such pipe or casing into or out of a well.
2. Description of the Prior Art
In prior arrangements for manipulating drill pipe or well casing into or out of a well, the pipe gripping device, which may be a swivel and/or an elevator, is suspended from a traveling block located generally within a derrick structure. The traveling block in turn is suspended by multiple strands of cable from a crown block mounted at the top of the derrick. A single strand of the cable passes over the crown block down to the drum of a drawworks mounted on the derrick floor or just below it. Such an arrangment involves elements which are usually massive and expensive, and is inherently dangerous. The multiple strands of cable between the traveling block and the crown block, necessary in order to achieve a desirable mechanical advantage, as well as the fact that the cable is turned on the drawworks drum means that the cable itself is considerably longer than the height of the derrick. Consequently, in addition to whatever load of drill pipe or well casing is being lifted, the crown block must support the weight of the traveling block as well as that of considerable length of cable. The drawworks itself introduces special problems into drilling operations. With its usually great mass, the drawworks may be difficult to move and to raise to its working level in setting up a derrick. Furthermore, with its partially open face and spinning drum, the drawworks is a source of danger for the men working on the derrick.